HTML5 Canvas Tutorial

One of the most important instruments in a painters toolkit is their canvas. It gives them the freedom to express all kinds of feelings, impressions, ideas, and so forth, in almost unlimited variations and combinations. And that freedom can be restricted only by two thingsï¿½ their skill level and their imagination.

The situation in the web development world is similar. With the ongoing progress of HTML5 and its powerful specifications, web developers have gained the ability to do things that were impossible in the past. Drawing graphics and creating animations directly in the browser is now completely possible thanks to a technology called HTML5 Canvas.

What is HTML5 Canvas?

The canvas element is an element defined in HTML code using width and height attributes. The real power of the canvas element, however, is accomplished by taking advantage of the HTML5 Canvas API. This API is used by writing JavaScript that can access the canvas area through a full set of drawing functions, thus allowing for dynamically generated graphics.

What's so Great About HTML5 Canvas?

Here are some reasons you might want to consider learning to use HTML's canvas feature:

Interactivity. Canvas is fully interactive. It can respond to a user's actions by listening for keyboard, mouse, or touch events. So a developer is not restricted to only static graphics and images.
Animation. Every object drawn on the canvas can be animated. This allows for all levels of animations to be created, from simple bouncing balls to complex forward and inverse kinematics.
Flexibility. Developers can create just about anything using canvas. It can display lines, shapes, text, images, etc. with or without animation. Plus, adding video and/or audio to a canvas application is also possible.
Browser/Platform Support. HTML5 Canvas is supported by all major browsers and can be accessed on a wide range of devices including desktops, tablets, and smart phones.
Popularity. Canvas popularity is rapidly and steadily growing so there is no shortage of resources available.
It's a web standard. Unlike Flash and Silverlight, Canvas is open technology that's part of HTML5. And although not all of its features are implemented in all browsers, developers can be certain canvas will be around indefinitely.
Develop once, run everywhere. HTML5 Canvas offers great portability. Once created, Unlike Flash and Silverlight, a canvas application can run almost anywhere from the largest computers to the smallest mobile devices.
Free and accessible development tools. The basic tools for creating HTML5 canvas applications are just a browser and a good code editor. Plus, there are many great and free libraries and tools to help developers with advanced canvas development.

What Applications Can You Create with HTML5 Canvas?

OK, canvas is great. But what exactly can use it for? Let's see.

Gaming. The HTML5 Canvas feature set is an ideal candidate for producing all sorts of 2D and 3D games.
Advertising. HTML5 Canvas is a great replacement for Flash-based banners and ads. It has all the needed features for attracting buyers attention.
Data Representation. HTML5 can collect data from global data sources and use it to generate visually appealing and interactive graphs and charts with the canvas element.
Education and Training. HTML5 canvas can be used to produce effective and attractive learning experiences, combining text, images, videos, and audio.
Art and Decoration. With a little bit of imagination and canvas wide variety of colors, gradients, patterns, transparency, shadows, and clipping features, all kinds of artistic and decorative graphics can be drawn.

Now that we know why we should learn canvas, let's look at the basics of HTML5 Canvas and how to start using it.

Canvas Rendering Contexts

Every HTML5 canvas element must have a context. The context defines what HTML5 Canvas API you'll be using. The 2d context is used for drawing 2D graphics and manipulating bitmap images. The 3d context is used for 3D graphics creation and manipulation. The latter is actually called WebGL and it's based on OpenGL ES.

HTML5 Canvas Element Size vs. Drawing Surface Size

Besides the canvas elements width and height attributes, you can also use CSS to set the size of a canvas element. However, sizing a canvas element with CSS is not the same as setting the elementswidth and height attributes. This is because a canvas actually has two sizes: the size of the element itself and the size of the elements drawing surface.

When you set the elements width and height attributes, you set both the elements size and the size of the elements drawing surface; however, when you use CSS to size a canvas element, you set only the elements size and not the drawing surface. When the canvas elements size does not match the size of its drawing surface, the browser scales the drawing surface to fit the element.

Because of this, it's a good idea to use the canvas elements width and height attributes to size the element, instead of using CSS.

Understanding the Canvas Coordinate System

In a 2D space, positions are referenced using X and Y coordinates. The X axis extends horizontally, and the Y axis extends vertically. The center has a position x = 0 and y = 0, that can also be expressed as (0, 0). This method of positioning objects, used in mathematics, is known as the Cartesian coordinate system.

The Canvas coordinate system, however, places the origin at the upper-left corner of the canvas, with X coordinates increasing to the right and Y coordinates increasing toward the bottom of the canvas. So unlike a standard Cartesian coordinate space, the Canvas space doesn't have visible negative points. Using negative coordinates wont cause your application to fail, but objects positioned using negative coordinate points wont appear on the page.

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